Transfer box, grinding from front section

Hi,
2003 disco 2 td5 auto
i have a load noise coming from the front of the transfer box, i have removed the front prop shaft, put it into diff lock, the rear wheels move ok but loud grinding from the front section.
My question is, how hard is it to rebuild this unit myself, i have a little workshop and basic garage tools.
thanks

Sadly......
where is the sorely missed @jamesmartin ?????

The front output housing is easy with some good circlip pliers and a drift, plus usual hand tools. If its that section of the box that is gone.

There are some good Youtube videos from Trailer-fitters Toolbox, and Britannica Restorations on rebuilding the transfer boxes.